Photovoltaic module and method for producing same

ABSTRACT

A description is given of a photovoltaic module ( 1 ) in the form of a laminate, which as the core layer exhibits a solar cell system ( 2 ) and encapsulation materials ( 3, 3 ′) applied on both sides of the latter. According to the invention, at least one encapsulation material layer ( 3 ′) consists of a sealing layer ( 4 ′) and a barrier layer ( 6 ), which consists of a plastic film or a plastic film composite, and on which an inorganic oxide layer ( 7 ) separated out to the vapor phase is present.

The invention relates to a photovoltaic module in the form of alaminate, which exhibits a solar cell system along with encapsulationmaterials provided for it. A procedure for its manufacture is alsodisclosed according to the invention.

PRIOR OF THE ART

Photovoltaic modules are used for generating electrical energy fromsunlight. The energy is generated via the solar cell system, whichpreferably consists of silicon cells. However, these can only carry aslight mechanical load, so that they must be enveloped on either side byencapsulation materials. Encapsulation materials can be one or morelayers of glass and/or plastic films and/or plastic film composites.

Plastic film composites essentially comprised of polyvinyl fluoride(PVF) and polyethylene terephthalate (PET) are produced by the applicantunder the designation ICOSOLAR, and used to manufacture photovoltaicmodules in a vacuum-lamination procedure disclosed in WO-A1-94/29106. Inthese modules, the solar cell system is protected not only againstmechanical damage, but also against exposure to the elements, inparticular water vapor. An intermediate layer made out of aluminum isprovided in the ICOSOLAR film composite as a barrier layer against watervapor. However, the disadvantage to this layer is that it iselectrically conductive in conjunction with the solar cell system, sothat undesired outside currents in the photovoltaic module come about.

DESCRIPTION OF THE INVENTION

Therefore, the object of the invention is to provide a photovoltaicmodule of the kind mentioned at the outset which does not exhibit thisshortcoming, but is largely impermeable to water vapor.

This object is achieved according to the invention by means of aproposed photovoltaic module, characterized by the fact that at leastone encapsulation material layer consists of a sealing and barrierlayer, and that the barrier layer is made out of a plastic film or aplastic film composite, which is provided on the side facing the solarcell system with an inorganic oxide layer separated out of the vaporphase.

Another advantage to the photovoltaic module according to the inventionis that the inorganic oxide layer consists of the elements aluminum orsilicon, and is present in a thickness of 30 to 200 nm. The organicoxide layer also exhibits the advantage that it is permeable to lightbeams in the visible light wave range and near UV wavelength range,while it absorbs them at shorter wavelengths in the UV wavelength range.

The photovoltaic module according to the invention also exhibits theadvantage that the sealing layer is arranged between the solar cellsystem and the barrier layer, and preferably consists of ethylene vinylacetate (EVA) or ionomers.

According to the invention, the plastic film on which the inorganicoxide layer is deposited additionally consists of polyethyleneterephthalate (PET) or ethylene tetrafluoroethylene copolymer (ETFE).

Other advantages of the photovoltaic module according to the inventionare that the inorganic oxide layer faces the solar cell system, andcontacts the adjacent sealing layer directly or via a primer coat.

In addition, the inorganic oxide layer is enveloped by plastic films orcomposites on both sides according to the invention, wherein at leastone plastic film or one plastic film composite acts as the barrierlayer. In this case, the inorganic oxide layer advantageously contactsthe plastic films or composites via an adhesive layer and/or a hybridlayer comprised of organic/inorganic networks.

According to the invention, the inorganic oxide layer consists of SiOx,wherein the atomic ratio of silicon to oxygen x lies within a range of1.3-1.7.

The invention also relates to a procedure for manufacturing aphotovoltaic module, wherein it is beneficial for:

a) a plastic film or plastic film composite to be provided with aninorganic oxide layer separated out of the vapor phase,

b) a module stack comprised of the solar cell system and encapsulationmaterials to be layered in such a way that the sealing layers envelopthe solar cell system on both sides,

c) this module stack to be incorporated into a loading station of aprocess arrangement in which it is kept at a temperature below thedistortion temperature of the sealing layers,

d) the module stack to be transported to a vacuum laminator in thisarrangement, which is evacuated, and in which the module stack is heatedto the distortion temperature of the sealing layers, and

e) the composite formed out of the module stack, after ventilating thevacuum laminator without recooling, to be transported to a hardeningfurnace, in which the sealing layers are hardened, so that a laminate isformed as a photovoltaic module, which can be removed from thecontinuous process after recooling.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described based on FIGS. 1 to 4:

FIG. 1 shows the structure of the photovoltaic module 1 according to theinvention, which mainly consists of the solar cell system 2 and theencapsulation materials 3, 3′ enveloping the solar cell systems.

FIGS. 1a and 1 b show variants Ia and Ib of the layer structure I inFIG. 1.

FIG. 2 shows an arrangement 13 for laminating the layers shown in FIG. 1for manufacturing the photovoltaic module 1 according to the invention.

FIG. 3 shows the light permeability in different wavelength ranges of aplastic film vapor-plated with an inorganic oxide layer, which isprovided within the encapsulating materials 3, 3′.

FIG. 4 shows the extent to which the photovoltaic module 1 according tothe invention improves the barrier effect relative to water vapor due tothe oxide layer 7 separated from the vapor phase.

ONE WAY TO PERFORM THE INVENTION

The invention will now be described in more detail based on embodimentsand on FIGS. 1 to 4. As shown in FIG. 1 the solar system 2 is made outof a series of silicon cells 8, which are soldered in series to formgroups by means of bonding wires 9. The encapsulation material 3′consists of the plastic sealing layer 4′ and the plastic film or plasticfilm composite 6, which exhibits the oxide layer 7 separated out of thevapor phase on the surface facing the solar cell system 2. This layerstructure is designated with I. The encapsulation material 3 can be madeout of layer 5, for example, which can be a glass layer or plastic filmcomposite similar to 6, and a plastic sealing layer 4.

FIGS. 1a and 1 b additionally show variants Ia and Ib, which can replacethe layer structure according to I.

In variant Ia (FIG. 1a), the inorganic oxide layer 7 is connected withan additional plastic film or plastic film composite 11 via an adhesivelayer 10 and/or a hybrid layer comprised of organic/inorganic networks.

In variant Ib (FIG. 1b), the inorganic oxide layer 7 exhibits anadditional primer layer 12, which as a result establishes the connectionto the sealing layer for prime.

In a first procedural step, the barrier layer 6 exhibiting the inorganicoxide layer 7 is formed. In this case, the structure can be selectedbased on the following table, with the sequence running from the outsidein, i.e., in the direction of the solar cell system:

TABLE (Examples a-d)

Example a

Barrier layer 6: Composite comprised of polyvinyl fluoride (PVF),polyethylene terephthalate (PETP) in film form

Inorganic oxide layer 7: SiOx or Al2O3

Sealing layer 4′

Example b

Barrier layer 6: Plastic film comprised of ethylene tetrafluoroethylenecopolymer (ETFE)

Inorganic oxide layer 7: SiOx or Al2O3

Sealing layer 4′

Example c

Barrier layer 6: Composite comprised of PVF and PETP

Inorganic oxide layer 7: SiOx or Al2O3

Hybrid layer comprised of organic/inorganic networks 10′

Adhesive layer 10: e.g., polyurethane

Plastic film or plastic film composite 11: Polyvinyl fluoride (PVF),polyvinylidene fluoride (PVDF), Ethylene tetrafluoroethylene copolymer(ETFE), Poyethylene terephthalate (PETP)

Sealing layer 4′

Example d

Barrier layer 6: Composite comprised of PVF and PETP

Inorganic oxide layer 7: SiOx or Al2O3

Primer coat 12: e.g., polyurethane, ethylene vinyl acetate (EVA),polymethyl methacrylate (PMMA)

Sealing layer 4′

As evident from the table, the barrier layer 6 can consist of a singleplastic film according to Example b), and of a plastic film compositeaccording to Example a).

Preferably used as the sealing layers 4′ are ethylene vinyl acetate(EVA) films, which yield slightly during heat treatment, as a result ofwhich they become cross-linked, which prevents the plastics fromcreeping.

Ionomers exhibit particularly good sealing properties. These arepolymers with ionic groups, which have a low water vapor permeability inaddition to good adhesive properties.

The inorganic oxide layer 7 is now generated on the PETP plastic film(see Example a) per table) in a thickness of 30 to 200 nm through vaporseparation under a vacuum (not shown). A vacuum coating system (notshown) is used to this end, for example. To ensure a satisfactoryadhesion between the plastic film surface and the inorganic oxide, thesurface of the plastic film is pretreated in a plasma consisting ofoxygen gas (99.995% purity).

Stoichiometric quantities of aluminum oxide (99.9% purity) or siliconmonoxide (99.9% purity) are used as the coating material, for example,and evaporated using electron beams under a vacuum. The energy usedduring evaporation measured 10 keV, for example, at an emission rate ofup to 220 mA. The thickness of the SiOx or Al2O3 layers can be setwithin a range of 30 to 200 nm by varying the evaporation rate or speedof the plastic films or plastic film composites moved via rollers.

For example, a speed of 5 m/min is selected in the laboratory forfabricating a 100 nm thick SiOx layer, while a speed of 2.5 m/min mustbe selected to manufacture a 40 nm thick Al2O3 layer. The evaporationrate here measured up to 70 nm/s; the pressure used during evaporationwas about 5×10−2 Pa. During industrial manufacture, speeds of 100 timesor more faster can be set.

The plastic film provided with the inorganic oxide layer, for examplemade out of PET, can now be laminated with the other plastic film formanufacturing the plastic film composite, for example made out of PVF(see Example a) per table).

The variants of the invention according to Examples a) and b) nowenvisage that the inorganic oxide layer 7, preferably a silicon oxidelayer, be in direct contact with sealing layer 4′, which ensures asatisfactory coupling. In this case, the atomic ratio between siliconand oxygen can be varied as desired.

However, if the inorganic oxide layer, preferably the silicon/oxidelayer, in the photovoltaic module according to the invention is intendedto additionally ensure a UV filtering effect, it is necessary to controlthe atomic ratio of silicon to oxygen during evaporation in such a waythat the share of oxygen x lies between 1.3 and 1.7.

In addition to the above criteria, e.g., selection of the startingproducts in a stoichiometric quantity ratio or evaporation speed, thiscan also be accomplished by additionally supplying oxygen in the form ofa reactive gas during evaporation. This gives rise to a highlytransparent oxide layer in the visible light wave range, which stillabsorbs UV rays, so that the UV-sensitive sealing layers 4′ are alsoprotected.

This is explained in greater detail in FIG. 3.

FIG. 3 shows the light permeability of an ETFE plastic film, whichexhibits a 320 nm thick SiOx layer as the inorganic oxide layer. Thismakes it evident that the SiOx coated plastic film is practicallyimpermeable to light in the UV range below 350 nm light wavelength. Anuncoated plastic film of the same constitution (not shown) would notabsorb light in this range, however. Starting at a light wavelength of350 nm, the ETFE film coated with SiOx starts to let the incident lightthrough. A significant transparence can be observed starting at about450 nm in the blue-violet portion of the spectrum of visible light. Ahigh transmission is observed over the remaining visible light range,which only diminishes again in the infrared range.

The following degrees of freedom are available to obtain properties ofthe photovoltaic module according to the invention, such as high lighttransmission in the visible and near-UV range given a simultaneousblockage of light in the shorter-wave UV range, and also a high barriereffect against water vapor:

1. Variation of inorganic oxide layer thickness:

In this case, light permeability can be advantageously influenced ingood approximation according to the Lambert-Beer's Law

ln(I/IO)=−4pkdl−1

where

I=light intensity allowed through

IO=radiated intensity,

k=wavelength-dependent absorption coefficient,

d=layer thickness of vapor-deposited inorganic oxide layer,

λ=light wavelength.

2. Variation of oxygen content (x) in the inorganic oxide layer,preferably SiOx layer:

If x is increased from the value of 1.3 according to FIG. 3 using othervapor-deposition conditions, the transmission of the material will behigher by the wavelength range of 400 nm without having to change thelayer thickness.

Values for x of 1.7, for example, can be set by adding oxygen whilesimultaneously incorporating electromagnetic energy in the form ofmicrowave radiation.

Therefore, varying the layer thickness and oxygen content parametersenable the simultaneous optimization of values for transmission in thevisible light range, the barrier effect in the ultraviolet range, andthe barrier effect relative to water vapor.

In addition to the selective atomic ratio of silicon to oxygen,resistance to atmospheric corrosion during outside use of thephotovoltaic module according to the invention is also ensured byenveloping the inorganic oxide layer 7 on both sides with plastic filmsor plastic film composites.

In FIG. 1, variant Ia, for example, this is done by having the barrierlayer 6 exhibit the inorganic layer 7, which in turn is in contact withanother plastic film or plastic film composite 11 via adhesive layer 10.In this case, adhesive layer 10 can be provided alone or in combinationwith a layer 10′ comprised of hybrid layers of inorganic/organicnetworks. These networks are inorganic/organic hybrid systems based onalkoxy siloxanes, for example. They exhibit a close crosslink density,and hence a high barrier effect relative to water vapor, and at the sametime adhere satisfactorily to the SiOx layer.

Further, the plastic films according to Example c) can becorrespondingly selected from the table, so that they additionally actto protect the solar cell system against exposure to the elements. Inthis case, the arrangement for the solar cell system according to FIG.1/Ia can also be selected in such a way that the barrier layer 6 isadjacent to the sealing layer 4′, while the plastic film or plastic filmcomposite 11 forms the outermost layer in the module stack.

In addition, it is also possible to bring about a satisfactoryresistance to atmospheric corrosion using a primer coat 12 made out ofplastic, which is arranged between the sealing layer 4′ and theinorganic oxide layer 7 according to FIG. 1/variant Ib and Example d)from the table.

All variants can now be used in the laminating procedure with the helpof arrangement 13 according to FIG. 2 in order to produce thephotovoltaic module 1. This arrangement shows the loading station 14 atwhich the module stack 1 can be placed on the carrier plate 15 moved bythe transport system 16, as well as the vacuum laminator 17 with thefixed upper part 18 and lower part 19 that can be raised and loweredusing the hydraulic arrangement 20. Temperature, pressure and retentiontime are set in the vacuum laminator 17 via control system 22. Inaddition, FIG. 2 shows the hardening furnace 23, whose temperature isset via control system 24, the cooling area 25, whose temperature can beset via control system 26, and the removal area 27.

One variant will now be presented as an example.

The barrier layer 6 provided with the inorganic layer 7 is layered withthe plastic sealing layer 4′, the solar cell system 2, another plasticsealing layer 4 and the glass layer 5, as shown in FIG. 1. A PET/PVFplastic film composite can be used in place of the glass layer 5.

Further, the layer 5, in particular when used outside, must be resistantto atmospheric corrosion and decorative, so that decorative laminatesheets provided with an acrylate layer and designed MAX® EXTERIOR aresuitable.

This module stack is now incorporated into the arrangement 13 forlamination according to FIG. 2. In this case, the module stack 1 isplaced on the carrier plate 15 at the loading station 14, which is keptat room temperature, or a maximal temperature of 80° C.

The top and bottom side of the module stack is provided with separatingfilms (not shown) to prevent adhesion to the carrier plate 15 andremaining system parts.

After the module stack 1 has been placed on carrier plate 15, the latteris conveyed into the vacuum laminator 17 via the transport system 16,for example a chain conveyor. The temperature of the heating plate 21 iskept at a level therein corresponding to the softening point of theplastic materials used in the sealing layer by means of an externalcontrol system 22. The hydraulic arrangement 20 presses the heatingplate 21 against the carrier plate 15, so that the flow of heat insidethe carrier plate brings the plastics sealing layers 4, 4′ in the modulestack to their softening point.

After the laminator 17 is closed, the external controller 22 applies avacuum. The evacuation removes air and other volatile constituents fromthe module stack, thereby ensuring a blister-free laminate. This isfollowed by ventilation, which presses the flexible membrane (not shown)against the module stack.

After a defined retention time of the module stack 1 inside the vacuumlaminator 17, the latter is ventilated, and the module stack istransported into the hardening furnace 23 without any additionalpressing power. The latter is kept at a defined temperature therein bythe control system 24, so that the sealing layers in the module stackharden after a defined retention time, and a laminate is formed that issubsequently cooled to room temperature in the cooling area 25. Thehardened laminate is take off of the carrier plate in the removal area27, and the recooled carrier plate can be routed back to the loadingstation 14.

The photovoltaic module 1 according to the invention can exhibitso-called thin-film solar cells instead of the crystalline siliconcells. In this case, the solar cell system can be connected with theencapsulation materials 3, 3′ via press molding or calendaring. Thesethin-film solar cells are not susceptible to breaking, they aresusceptible to water, which makes the solution proposed in the inventionparticularly worthwhile.

The photovoltaic module stack can have the following structure, forexample:

Example e):

Layer 5: Glass Solar cell system 2: Thin-film solar cell made out ofamorphous silicon Sealing layer 4′: EVA Barrier layer 6: ETFE plasticfilm with inorganic SiOx oxide layer 7

Example f):

Layer 5: Glass Solar cell system 2: Thin-film solar cell made out ofamorphous silicon Sealing layer 4′: EVA Barrier layer 6: PVF/PET plasticfilm composite and inorganic SiOx oxide layer 7

In Examples e) and f), the thin-film solar cell system is protectedagainst water vapor by the barrier layer 6. However, since the latter isnot susceptible to breaking, the additional sealing layer 4 can beomitted.

COMMERCIAL APPLICABILITY

The photovoltaic modules fabricated with the procedure according to theinvention are used for generating electrical energy out of sunlight.They have various applications, ranging from small power plants foremergency call boxes or mobile homes via structurally integrated roofand facade systems, to large-scale plants and solar power facilities.

With respect to outside applications, it has been shown that the barriereffect relative to water vapor is significantly improved by the oxidelayer separated out of the vapor phase. FIG. 4 explains this in greaterdetail.

In this case, uncoated films (left column on abscissa) were comparedwith SiOx coated films (right column on the abscissa) with respect totheir water vapor permeability in g/m2d.

As evident from this comparison, the water vapor permeability could bereduced to about one tenth the value of the uncoated material for typeRN 12 PET, and to 1/25 for type RN 75. The water vapor permeability iseven reduced by a factor of about 100 for ETPE with a material thicknessof 20 μm.

What is claimed is:
 1. A photovoltaic module in the form of a laminate,which as the core layer exhibits a solar cell system and encapsulationmaterials applied on both sides of the latter, wherein at least oneencapsulation material layer comprises a sealing layer and a barrierlayer, and that the barrier layer comprises a plastic film or a plasticfilm composite, which exhibits an inorganic oxide layer separated out ofa vapor phase by physical vapor deposition and said sealing layer isarranged between said solar cell system and said barrier layer.
 2. Aphotovoltaic module according to claim 1, wherein the inorganic oxidelayer contains the elements aluminum or silicon, and is present in athickness of 30 to 200 nm.
 3. A photovoltaic module according to claim1, wherein the inorganic oxide layer is permeable to light beams in thevisible light wave range and near UV wavelength range, while it absorbssaid beams in the UV wavelength range at shorter wavelengths.
 4. Aphotovoltaic module according to claim 1, wherein the sealing layerconsists of ethylene vinyl acetate (EVA).
 5. A photovoltaic moduleaccording to claim 1, wherein the sealing layer consists of ionomers. 6.A photovoltaic module according to claim 1 wherein the plastic film onwhich the inorganic oxide layer is deposited consists of polyethyleneterephthalate (PET) or ethylene tetrafluoroethylene copolymer (ETFE). 7.A photovoltaic module according to claim 1 wherein the inorganic oxidelayer faces the solar cell system and directly contacts the adjacentsealing layer.
 8. A photovoltaic module according to claim 1, whereinthe inorganic oxide layer faces the solar cell system and contacts theadjacent sealing layer via a primer coat.
 9. A photovoltaic moduleaccording to claim 1, wherein the inorganic oxide layer is enveloped onboth sides by plastic films or composites, wherein at least one plasticfilm or plastic film composite acts as the barrier layer.
 10. Aphotovoltaic module according to claim 9, wherein the inorganic oxidelayer contacts the plastic films or composites via an adhesive layerand/or a hybrid layer comprised of organic/inorganic networks.
 11. Aphotovoltaic module according to claim 1, wherein the inorganic oxidelayer consists of SiOx, wherein the atomic ratio of silicon to oxygen xranges from 1.3 to 1.7.
 12. A procedure for manufacturing a photovoltaicmodule according to claim 1, comprising: a) providing a plastic film orplastic film composite with an inorganic layer separated out of thevapor phase by physical vapor deposition, laminating said plastic filmor plastic film composite provided with said inorganic layer withsealing layers in order to form encapsulating materials, b) forming amodule stack out of the solar cell system and the encapsulationmaterials in such a way that the sealing layers envelop the solar cellsystem on both sides, c) introducing this module stack into a loadingstation of an arrangement in which it is kept at a temperature below thesoftening point of the sealing layers, d) transporting the module stackto a vacuum laminator, which is evacuated, and in which the module stackis heated to the softening point of the sealing layers, and e) after thevacuum laminator has been ventilated without recooling, transporting thecomposite formed out of the module stack into a hardening furnace, inwhich the sealing layers are cured, so that a laminate in the form of aphotovoltaic module is formed, which is removed after recooling.